(1) Field of the Invention
The present invention relates to an automatic temperature adjusting type air conditioner particularly used for an automotive vehicle passenger compartment which carries out independently air flow rate adjustments for a blowing fan and an angular movement adjustment for an air mixing door using only a single power servomechanism.
(2) Description of the Prior Art
In recent years, on most automotive vehicles an air conditioner has been mounted to provide warm air or cooled air within the passenger compartment.
Such an air conditioner, in general, comprises a duct, a blowing fan, an evaporator located downstream of the fan, and a heater core through which engine cooling water is circulated. Furthermore, downstream of the evaporator an air passage is provided for bypassing the heater core and an air mixing door is provided at a branch portion between the heater core and its bypass passage for controlling the air flow passage. An air mixing chamber is formed downstream of the bypass passage from which the conditioned air is blown into the passenger compartment through a plurality of ventilators.
An such an air conditioner of an automatic temperature adjusting type has been proposed which maintains the temperature and humidity within the passenger compartment comfortable.
In other words, the air mixing door is operated by a linkage driven by a power servomechanism. A fan switch is provided to control the air flow rate of the fan according to the stroke at which an extendable arm attached to the power servomechanism is extended.
The power servomechanism is connected to a transducer such as a double solenoid vacuum valve having two electromagnetic valves; one of which is connected to a vacuum source such as a vacuum tank and the other connected to the atmosphere. The double solenoid vacuum valve controls a vacuum pressure to be conveyed to the power servomechanism depending on the voltage energizing the solenoid thereof. The energizing voltage is in turn controlled by a plurality of temperature sensors located, e.g., inside and outside the passenger compartment. These temperature sensors detect the air temperature by the change in their resistances with respect to the temperature. Input terminals of an automatic temperature adjusting amplifier are connected to these sensors and to a temperature setting resistor to compare the voltages between them. Thus when the difference exists in the compared result, the output voltage according to the difference is fed into the double solenoid vacuum valve so that the vacuum pressure to be conveyed to the power servomechanism is changed.
When the temperature adjustment and dehumidification are performed within the passenger compartment, both evaporator and heater core are operated and simulataneously the air mixing door is swung up at a suitable angle. Under such condition, the fan introduces fresh air into the duct and the evaporator cools and dehumidifies the air. Part of the cooled air is passed through the heater core to raise the temperature. After mixing the cooled air flowing through the bypass and warm air flowing through the heater core in the air mixing chamber, the mixed and conditioned air is blown out of the ventilators into the passenger compartment. The rate of air flow through the blowing fan is the greatest at the maximum or minimum stroke position of the power servomechanism and the fan switch is predetermined so that the amount of air flow gradually decreases toward the center position of the power servomechanism.
However, in such a conventional automatic temperature adjusting type air conditioner, the cooling function is often performed using only cooled air from the evaporator passing through the bypass passage. At this time, the air mixing door is in the maximum cooling position; in other words, the cooling function is performed with the cooled air from the evaporator not passing through the heater core. When the power servomechanism is operated with the passenger compartment gradually cooled, the amount of air flow from the fan is gradually reduced and the air mixing door is swung from the maximum cooling position to an air mixing position. In other words, part of the cooled air is passed through the heater core, thus sharply reducing the cooling capability. Since the power servomechanism is again operated to cool the passenger compartment to meet a temperature set by the driver, hunting tends to develop. Such hunting seriously reduces the efficiency of cooling the passenger compartment.
Hunting also develops when the air mixing door is in the maximum heating position; in other words, when the power servomechanism is operated to cool the passenger compartment from the state in which the air mixing door closes the bypass passage.